I have a Finnish M39 Mosin Nagant that I bought from http://www.gunsnammo.com/ a while back. I have only fired a handful of rounds through it, and I took the first few empty shells along with the rifle to my local gunsmith to have it checked for safety. He didn't have the right headspace gauge for my rifle but from looking it over and examining the shells, he said it seemed OK.

So yesterday I took it down the rifle range again after a few months of a break, and the second round I fired, the shell was cracked near the shoulder. The crack was longitudinal, and just a few millimetres long. There were no signs of any cracks near the rim.

Is this dangerous? I was afraid to fire any more once I saw this, but maybe it's normal for cracks to appear on the shoulder of the cartridge, I don't know. Any advice would be greatly appreciated!